Long-read single-cell genome, transcriptome and open chromatin profiling links genotype to phenotypes.

Current single-cell multiomics methods typically provide limited genomic information, constraining genotype-phenotype studies. To address this gap, we developed SPLONGGET (Single-cell Profiling of LONG-read Genome, Epigenome, and Transcriptome), which integrates 10X Genomics barcoding with Oxford Nanopore sequencing to simultaneously profile genome, chromatin accessibility, and full-length transcriptomes in thousands of single cells. By retaining all tagmentation fragments during library preparation, SPLONGGET delivers whole-genome coverage, supports target enrichment for effective single-cell genotyping, and remains backwards compatible with existing short-read workflows. SPLONGGET enables comprehensive calling of small variants, structural variants, and copy number alterations. Applying SPLONGGET to paediatric B-cell acute lymphoblastic leukaemia revealed clonal dynamics and the phenotypic effects of somatic variants. Notably, we evidence parallel evolution of immune escape variants with four distinct splice site mutations and loss of heterozygosity in the CAR T-cell therapy CD19 target. In conclusion, SPLONGGET enables integrated high-throughput analysis of genetic variation and molecular phenotypes using off-the-shelf kits, offering a timely and powerful tool to study genetically heterogeneous samples, such as tumours but also ageing normal tissues.